This invention relates to an air-cylinder apparatus for use in a prosthetic limb designed for assisting the bending and stretching motion of an amputee""s knee and more particularly to a technique capable of generating a proper resisting force in accordance with the bending motion of the knee when a prosthetic limb is in a swing phase in walking in which the prosthetic limb is left from a grounding surface such as, a floor surface.
Prosthetic limbs accompanying the bending and stretching motion of the knee are prosthetic limbs in which a femoral member and a crus member are oscillated relative to each other. Among them, there are prosthetic limbs of the type which includes an auxiliary apparatus for assisting the bending and stretching motion of the knee in order to attain a walking style (walking attitude) resembling a natural walking style. As the auxiliary apparatus, there are known a hydraulic cylinder apparatus and an air-cylinder apparatus. Comparing the two different types of cylinder apparatuses as an auxiliary apparatus, oil as working fluid of the hydraulic cylinder has almost no compressibility, while air as working fluid of the air-cylinder apparatus has compressibility. Therefore, with the use of the air-cylinder, there can be obtained a repulsive energy after the knee is bent to the maximum extent by the compressed energy generated by compression of air.
The specification of Japanese Patent Publication No. S52-47638 and FIGS. 2 and 3 of U.S. Pat. No. 5,405,407 show a first technique of an air-cylinder apparatus for use in a prosthetic limb. This technique includes a check valve within a piston and a needle valve as a throttle valve within a piston rod. Those valves are actuated to compress a chamber within the air-cylinder when the knee is bent and the flow of air out of the chamber is restricted by the throttle valve. However, the flow of air is restricted by a single throttle valve and the degree of opening of the throttle valve is kept constant during walking. For this reason, the bending motion of the knee cannot be controlled appropriately in accordance with walking speed. This follows that the first technique cannot cope with such a wide range of walking speed as slow walking, normal walking, fast walking and tripping.
In contrast, Japanese Patent No. 2,501,346 and U.S. Pat. No. 5,344,446 based thereon discloses a technique for adjusting the degree of opening of a throttle valve for restricting the flow of air in accordance with walking speed using a computer. This second technique can control the bending motion of the knee appropriately in accordance with walking speed. The wearer of the prosthetic limb can attain a natural walking attitude over a wide range of walking speed. However, this second technique has such shortcomings in that each means for controlling and driving is necessarily required for adjusting the throttle valve automatically and therefore, the prosthetic limb becomes complicated in structure and increased in cost.
In order to attain a natural walking attitude over a wide range of walking speed while restraining increase in cost, it can be contemplated to make the prosthetic limb entirely mechanically in structure without a need of a provision of a computer for controlling. A third technique, which is disclosed by National Publication No. H08-511190 (corresponding to WO95/26171) and U.S. Pat. No. 5,092,902, can be applied to an air-cylinder apparatus, although the third technique is directed to a hydraulic cylinder apparatus and not to an air-cylinder apparatus. In the third technique, the throttle valve is provided with a plurality of throttle holes arranged in a direction of movement of a piston such that the throttle valves are sequentially closed in accordance with movement of the piston. According to this technique, resisting force against flow can be enlarged by intensifying the throttling action of the throttle valve as the bending degree of the knee is increased. However, because a throttle area is, either digitally or steppingly, varied in accordance with movement of the piston, pressure characteristics of the cylinder are also steppingly varied, thereby deteriorating the wearer""s feeling of walking. Moreover, in this type of a cylinder for use in a prosthetic limb, it is necessary to adjust the pressure characteristics of the cylinder for each wearer. In the case where there is a provision of only one pressure chamber, it is difficult to meet with the requirement for adjustment of the pressure characteristics of the cylinder for each wearer.
It is, therefore, a first object of the present invention to provide an air-cylinder apparatus for use in a prosthetic limb in which pressure characteristics can effectively be adjusted over a wide range of walking speed.
It is a second object of the present invention to provide an air-cylinder apparatus for use in a prosthetic limb in which a natural walking attitude can be obtained in a wide range of walking speed without deteriorating the wearer""s feeling of walking.
A third object of the present invention is to provide an air-cylinder apparatus for use in a prosthetic limb in which a throttle valve portion is stable in construction so that an accurate pressure controlling can assuredly be obtained in accordance with walking speed.
To achieve the above objects, the way the inventor(s) of the present invention thought is as follows. Basically, the interior of a cylinder body is divided into two chambers by a piston as in the related art. The divided chambers include a first chamber which is located on the head side and a second chamber which is located on the bottom side. The first and second chambers are communicated with each other through two passages. The first passage includes a first check valve for permitting a flow of air from the first chamber towards the second chamber. By permitting the flow of air from the first chamber towards the second chamber, the first passage enables the knee to be bent and besides, the first check valve confines the air, which has flowed into the second chamber, therein. The second passage includes a constant throttle valve for normally restricting a flow of air from the second chamber towards the first chamber. The constant throttle valve has the role for normally restricting the flow of air from the second chamber towards the first chamber even when the bending state of the knee is changed.
An air-cylinder apparatus for use in a prosthetic limb according to the present invention further comprises, in order to increase an internal pressure of the second chamber when the knee is bent, the following component elements.
(A) division means for dividing the second chamber, which is located on the bottom side, into plural chambers including a predetermined chamber confronting an opening for intercommunicating the second chamber with the constant throttle valve in accordance with increase in bending angle of the knee, the division means being provided at a bottom part of the cylinder body with a projection or a recess and at one surface, facing the bottom part, of the piston with a counterpart projection or a recess; and
(B) an auxiliary passage for communicating each and all of the plural chambers divided by the division means only excluding the predetermined chamber with the first chamber through throttle valves, respectively.
In the air-cylinder apparatus for use in a prosthetic limb according to the present invention, it is not only arranged such that the flow of air out of the second chamber, in which air is confined in accordance with the bending motion of the knee and internal pressure is increased, by the constant throttle valve but also that the second chamber is divided into plural chambers in accordance with increase in bending angle of the knee and air is restricted from flowing out of those divided chambers by throttle valves corresponding to the divided chambers. The divided plural chambers include not only the predetermined chamber confronting the opening for communication with the constant throttle valve but also other chambers concentric therewith. In order to accurately control the pressure characteristics over a wider range of walking speed, an increased number of divisions is preferable. Actually, the number of divisions is 2 to 5 and normally, the proper number of divisions is 2 to 3. The time point for dividing the second chamber into plural chambers can properly be changed in accordance with the number of divisions. In the case where the number of divisions is 2, the time point for division is at a stage where a bending angle of the knee exceeds 40 to 60 degrees (for example, 50 degrees) for normal walking. In the case where the number of divisions is 3, the time point is not only at a stage where the bending angle exceeds, for example, 50 degrees as mentioned but also at a stage where the bending angle is smaller, for example, 30 degrees, than 50 degrees. At the respective time points, the piston and the bottom part of the cylinder body are engaged with each other through the projection and the recess, thereby defining new chambers within the second chamber. In order to hermetically close the newly defined chambers, the engagement projection and recess are provided with a seal member such as a lip type seal ring. In order to generate a higher pressure in the second chamber at the time of faster walking speed, in addition to a provision of the constant throttle valve, the second passage is preferably provided with a second check valve for permitting the flow of air from the second chamber towards the first chamber and for prohibiting the flow of air in the reversed direction.
Most preferably, the throttle valve of the auxiliary passage is communicated with the first chamber through the predetermined chamber and the constant throttle valve. By doing so, the throttle valves for the newly divided chambers defined within the second chamber are interposed between the predetermined chamber and the newly divided chambers. Since pressure is generated, under the effect of the constant throttle valve, in the predetermined chamber prior to the time point for division, pressure in the newly divided chambers is not increased abruptly. As a result, due to characteristics of the air-cylinder apparatus, a repulsive force is not generated abruptly but it is generated gradually. For this reason, the wearer of the prosthetic limb can walk with a feeling of natural walking without a sense of incompatibility.
As the constant throttle valve and the throttle valve, various kinds of throttle valves can be used. Among them, a screwing type needle valve is most preferable. The screwing type needle valve is properly adjusted in opening degree through rotation of the screw (i.e., by converting a rotary motion to a linear motion) and can be used as a fixed throttle valve having a constant throttling amount. Since the fixed throttle valve is of a construction in which no movable valve body and no spring is used, a stable controlling can be made in a movable prosthetic limb.